This invention relates to home canning closure systems and more particularly it relates to an improved home canning closure system featuring a plastic ring and a metal lid combination which is adapted to allow excess pressure to escape while preventing the escape of the contents of the container.
Closure systems for a home canning jar have traditionally comprised a metal lid and a metal ring which fits over the metal lid and incorporates threads adapted to engage mating threads in the jar. The metal lid serves to seal or close the open mouth of the jar, and the metal ring serves to hold the metal lid in place until such time as a vacuum is created in the jar. The metal ring also provides a protective cover to prevent dislodging of the metal lid after the creation of a vacuum in the jar which holds the metal lid in place.
A sterilized home canning jar is filled with the product being canned while hot and then a sterilized metal lid is placed thereover and a metal ring is then threaded into engagement with the canning jar to hold the metal lid in sealing engagement with the jar. As the product cools, a vacuum is created in the headspace above the product in the jar which then holds the metal lid in sealing engagement with the jar. In the home canning of certain products, the jar is partially or fully immersed in boiling water after it has received the hot product and the closure system. This continued heating of the package creates increased pressure within the jar which must be allowed to escape. Thus, the metal lid and metal ring will flex slightly to allow some pressure to escape from the jar.
However, the metal rings have been found to have a rather short life span due to corrosion and rust. Even if they are re-used, they have a rather unpleasant appearance.